Michelson interferometers have been used, in various devices, for the measurement of displacement, spatial non-uniformity, angle, and polarization states of various reflecting bodies. Typical Michelson interferometer devices utilize a gas laser to produce a beam of monochromatic light which is then split into signal and reference beams. The signal beam is transmitted to and then reflected from a target body. The signal and reference beams are recombined in the device into a composite, co-linear beam. The difference in phase between the two beams creates an interference pattern, or fringe pattern, in the composite beam which is extremely sensitive to change in the position of the target body. Hence, information about the dynamics of a target body can be determined by study of the dynamics of the interference pattern.
In such interferometer devices, the signal and reference beams must be precisely re-aligned into a linear composite beam in order to maximize the signal-to-noise ratio, or contrast, of the interference pattern. Current interferometer designs require precision optical components and extremely stable mechanical structures to achieve this precise alignment. Moreover, such designs utilize more components than necessary, thereby increasing the complexity and reducing the reliability of the devices. As a result, such interferometer devices are relatively expensive to manufacture, calibrate, and maintain.
One difficulty with the Michealson interferometer is the problem of keeping the reference and the signal light beams in exact parallel and colinear alignment. This is required in order to obtain the highest contrast or signal-to-noise ratio. Even with good initial alignment, small vibrations or temperature changes can result in distortion or beam shifting resulting in beam misalignment. The present invention uses an adaptive method such that any small shift or movement of the optical components is of little importance. That is, the reference beam and signal beam will remain colinear over small movements or rotations of the optical components.
For example, in the original Michealson device, two flat mirrors and a beam splitter are used. The alignment of these optical components is very critical. Any small rotation of a flat mirror can cause the two beams to diverge. Improvement can be made by replacing the two flat-mirrors by two corner-cubes which will reflect light back at exactly the same angle even if the corner-cube is rotated slightly. In this way, the alignment of the two reflectors in the Michealson interferometer becomes less critical. However, the alignment of the beam splitter is still very critical. Any small rotation of the beam splitter will cause the reference beam and the signal beam to become divergent.
The present invention solves this problem by using the laser output mirror as part of the interferometer to combine the reference and signal beams. As shown in FIG. 1, by using a corner cube as the means for reflecting the source beam, and the output mirror of the laser itself for steering the reflected beam to the splitter, the two beams must always be colinear even if the splitter is rotated over a small angle.
There is a need for an improved interferometer device that contains a minimal number of components, fewer of which require extreme precision or extremely stable mechanical structures. The present invention fulfills these needs and provides further related advantages.